Agriculture Reference
In-Depth Information
period (EPP) determined by the longevity of the egg apparatus minus the time
necessary for pollen tube growth. This is measured by carrying out controlled
pollination at daily intervals from anthesis for as long as the stigmas remain
receptive.
Cultivars differ in EPP duration. Although the EPP varies with a number of
other factors differences between EPPs of cultivars under broadly comparable
conditions have been found in a number of studies. Williams (
) reported
EPPs of about
.
,
.
and
.
days for 'Cox', 'Jonathan' and 'Laxton's Superb'
apples, respectively, and of
days for 'Doyenne du Comice',
'Packham'sTriumph','Williams'BonChretien'and'Conference'pear,respec-
tively. Tromp and Borsboom (
,
,
and
-
) noted a much shorter EPP for 'Comice'
than for 'Golden Delicious' which showed high levels of fruit set when polli-
nated to
days after bloom. 'Red Delicious' has a short EPP, Hartman and
Howlett (
) noting a linear decline in its fruit set when pollination was
delayed from
hours after anthesis. Some cultivars also suffer from con-
sistently asynchronous flower part development. Herrero (
to
) found that
'Agua de Aranjuez' pear flowers have delayed maturation of the megagameto-
phytes in relation to anthesis. Stigmas were not receptive at anthesis and no
mature embryo sacs were present then, most of them being fully mature
days
later.
Although largely controlled by genotype, female fertility also varies greatly
from year to year (Williams,
) and has been shown to be influenced by a
number of separate factors operating at different times, from flower initiation
and development in the previous year to anthesis and beyond.
The application of nitrogenous fertilizer after the cessation of apple shoot
growth leads to the production of 'strong' blossoms that develop earlier than
those on control trees (Williams,
). The ovules of these flowers remain
capable of fertilization for almost twice as long as those of 'normal' flowers.
Heavy cropping in the previous season results in smaller flowers, less well
expanded papillae on stigmas and thinner styles of 'Cox' apple (Buszard and
Schwabe,
). Such flowers failed to set fruit if pollinated at anthesis and no
fruits set after day
days, whereas flowers on previously
defruited trees set fruit when pollinated on any day from anthesis to day
, i.e. the EPP was
,
i.e. had a
-day EPP.
Flowers on young wood and on young trees of apple have shorter EPPs and
higher proportions of immature and of degenerate ovules than those on older
woodandtrees(RobbieandAtkinson,
).Theseeffectsseemtoberelatedto
thetimingofflowerinitiationanddevelopment,physiologically'young'flowers
being of lower quality than older ones. Flowers on horizontal branches have
a higher proportion of healthy ovules at anthesis and later and have a longer
EPP than those on vertical branches (Robbie
et al.
,
). This quite large effect
could be achieved by bending branches that had been vertical into a horizontal
